#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    long long n;
    cin>>n;
    long long a[n],b[n];
    for(long long i=0;i<n;i++)cin>>a[i];
    for(long long j=0;j<n;j++)cin>>b[j];
    double s1=0,s2=0;
    for(long long k=0;k<n;k++){
        s1+=double(a[k]);
        s2+=double(b[k]);
    }
    s1*=3;
    s2*=2;
    s1-=s2;
    double s3=0;
    for(long long u=0;u<n;u++)s3+=double(a[u]-b[u]);
    cout<<fixed<<setprecision(6)<<s1/s3;
    return 0;
}

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